Conventional technology of natural gas processing requires many separation steps, from acid gas removal (“sweetening”) to heavier hydrocarbon recovery, nitrogen rejection and drying. Before the natural gas is delivered for urban and industrial use or LNG production, among other uses, usually the natural gas liquids (NGLs) such as ethane and C3+ hydrocarbons are also separated for other uses. The biggest drawback of the conventional gas processing is that these steps demand large consumption of energy. Gas processing is usually done by exposure of the natural gas to amines to remove acid gases (CO2 and H2S), glycol units to remove non condensable water, and membranes to remove nitrogen, for example. In turn, NGLs are separated using costly cryogenic processes.
In conventional gas conditioning technologies, several step-wise processes are required to isolate the many constituents of natural gas coming from the wellhead. Water comes with the oil and gas when exiting the well, so the first process is the removal of the liquid water. Following flash separation, the natural gas stream is sent to an amine unit where hydrogen sulfide and carbon dioxide are removed (the “sweetening” step). It is important to remove acid gases such as these due to their toxic, corrosive nature. In addition, many components, especially CO2 alter the heating value of natural gas and their composition is regulated. A common side process directs the isolated acid gases containing H2S to a Claus unit where sulfur can be recovered in its elemental form. The now sweetened natural gas then has to be dehydrated. Usually, the next step is nitrogen removal using either pressure-swing adsorption, or membranes. Although nitrogen is not corrosive, its removal is still needed since N2 lowers the heat value of the natural gas. After nitrogen rejection, the natural gas is primarily composed of hydrocarbons ranging from methane up to pentane and minor amounts of heavier hydrocarbons up to octane. Although these are typical components found in natural gas, the exact gas make-up depends highly on its source. Methane is the primary component of natural gas that is sold to consumers, so it is isolated next using a cryogenic distillation process, called a demethanizer unit. The methane-free natural gas liquids are then sent to an ordinary fractionation column, called a deethanizer, to recover ethane in the distillate followed by at least two other columns to separate heavier components (propane, butane, pentanes, and sometimes heavier hydrocarbons). Clathrate hydrate formation has been employed previously in certain treatments of natural gas.
As noted above, a major drawback of conventional gas processing (for example removal of acid gases by amines) is that these steps demand large consumption of energy. A method for purification of natural gas which consumes considerably less energy and significantly reduces the operation costs and loss of methane conventionally involved in removal of contaminant gases, and which is more environmentally-friendly, would be desirable. It is to such a method that the present disclosure directed.